Hello! I've performed a few simple tests using Haskell and C++ on primitives. I've compilled all Haskell programs with -O2 optimizations, and C++ ones with -O3 ghc version - 7.10.2, gcc version : 5.1.1 I'm sending the codes in the zip file. *Problem1* - 100 000 000 iterations. Time of execution (in seconds): *Int pure tail recursion*: 6.911011299962411e-2 *Int# pure tail recursion *: 4.587398100011342e-2 *IORef for loop* 1.1533970820000832 *IORef 'tail' recursion* 1.0696569040001123 *STRef for loop* 1.1545546840006864 *STRef tail recursion* 1.1110019479992843 *C++ *: 2.7e-07 The llvm version could be as fast as C++ one in this problem. Buuut... then there's *problem 2* (using if or case) - 100 000 000 iterations: *Int# tail recursion* 1.315346227000191 *IORef for loop*: 2.6442542390004746 *STRef for loop*: 2.669217500999366 *C++*: 0.158056 Here haskell is about 9 times slower than C++. *Problem 4* - executing the same functionality using bit operations - 100 000 000 iterations: *Int# tail recursion:* 0.12361123500068061 *C++:* 0.131141 So, Haskell here is as fast as C++. My question is: can IORefs and STRefs be optimized ? I would like very much to rely on them, but I would like to achieve great speeds. Also, is can one achieve good speeds of execution when using cases or ifs ? If not, what is the other way to do it ? Compiler flags, Cmm optimizations - they are all welcome. And the final question - how hard would it be to implement such optimizations in ghc compiler? Regards, Mateusz Kłoczko